The present invention relates generally to equipment and procedures used in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides a safety system for use in perforating operations.
Perforating typically involves use of explosive shaped charges in a perforating gun to form perforations or openings through casing cemented in a well. Detonation of the shaped charges is initiated by a device known as a firing head. The firing head may be operated mechanically, electrically, by application of pressure, via various forms of telemetry, etc.
For safety reasons, it would be desirable to isolate the firing head from the perforating gun prior to installing a perforating assembly in a well. Preferably, the firing head would also be isolated from the perforating gun while the perforating assembly is being installed and aligned with a zone to be perforated. In this manner, detonation of the shaped charges in the perforating gun could be avoided, even though the firing head might accidentally be operated, prior to the time when it is desired to perforate the zone.
Furthermore, it would be beneficial to retrieve the perforating gun from the well, without also retrieving the firing head at the same time, in the event that the firing head malfunctions. In this manner, accidental detonation of the shaped charges during retrieval of the perforating gun can be avoided.